You Can’t Transmute Enervation
The Transmuted Spell metamagic states the following:
When you cast a spell that deals a type of damage from the following list, you can spend 1 sorcery point to change that damage type to one of the other listed types: acid, cold, fire, lightning, poison, thunder.
Because the enervation spell deals necrotic damage, you can’t use this metamagic with the spell.
This might lead you to then ask, well what if we houseruled that you could use Transmute Spell with it? In that instance, yes, because you houseruled that you can (or probably should to keep it fun*).
The Transmute Spell metamagic simply changes the damage type, but it wouldn’t be unreasonable to extend that change to the healing text. The thematic reason for why this alternative damage type heals you is up to you as the player to decide if your table elects to allow this house rule.
If you elect to not houserule in that way, you wouldn’t be able to receive any healing on the initial casting. Subsequent reapplications of the damage would be necrotic because Transmuted Spell only changes the damage type when you cast the spell.
*I make this statement because enervation isn’t the only spell which would have this problem if you didn’t. It would also effect vampiric touch and life transference.